Improvements were evident if the subjects studied were not suffering from B vitamin deficiency, said the report published in Nutrients.
Analysing the results of 38 randomised or quasi-randomised controlled trials, the researchers from Seoul National University and Hallym University compared the effects of B vitamins, vitamin D, and antioxidant vitamins A, C, E on cognitive health.
Out of the 38 trials, 23 focused on B vitamins, nine on antioxidant vitamins, and six on vitamin D. All the subjects studied in the trials are were either healthy or were only suffering from mild cognitive impairment.
The researchers found out that B vitamins were the most beneficial, especially in strengthening the global cognitive function and episodic memory.
It was however, not of much aid in terms of improving cognitive domains such as processing speed, attention, and executive function.
On the other hand, antioxidant vitamins also exerted benefits for improving global cognitive function, albeit to a smaller extent than B vitamins.
As for vitamin D, there was no conclusive benefits seen. There was only one study which showed vitamin D intervention was beneficial for improving attention and visuospatial function.
The researchers explained that the B vitamins were beneficial because they could exert effects on the brain directly through their acute influence on hypomethylation and indirectly through their long-term influence on homocysteine levels.
The study was supported by funding from the Ottogi Ham Taiho Foundation.
However, the benefits of B vitamins would be reduced or even become insignificant if the supplementation took place over 12 months.
The researchers explained that the long-term cumulative effect of habitual dietary patterns and the physiological changes of study participants may mask the beneficial effect of B vitamins.
The researchers acknowledged that the analysis has a number of limitations.
Firstly, because the combination and dosage of supplementation varied across the clinical trials studied, this could have affected the findings of this particular meta-analysis.
For example, trials which only study vitamin B12 might have different results for those that are studying only vitamin B6 since different vitamins have different physiological functions.
“This could be a particular problem because of distinct physiological functions by the type of vitamins such as helping the synthesis of serotonin, dopamine, norepinephrine and gamma-aminobutyric acid (GABA) for folate (vitamin B9), aiding the synthesis, methylation, and repair of DNA for vitamin B6, and assisting the function and maintenance of nerve cells for vitamin B12,” the researchers said.
“However, because all three of these B vitamins are particularly important components for methylation when homocysteine is recycled into methionine and folate and vitamin B12 are dependent on each other for their activation, it could be worthwhile to treat them collectively and examine their effect in a single model.”
Also, they said they could not make definitive recommendations regarding the duration or dosage of the vitamin intake due to differences in study designs of the trials included in the meta-analysis.
Efficacy of Vitamins on Cognitive Function of Non-Demented People: A Systematic Review and Meta-Analysis
Authors: Ki Woong Kim and et al